Mechanism of the catalytic action of the mechanoactivated salt K2PTCL4 in the gas-phase hydrochlorination of acetylene

A heterogeneous catalyst for the hydrochlorination of acetylene by gaseous HCl is formed as a result of mechanical treatment of the solid salt K₂PtCl₄ in an atmosphere of acetylene, ethylene, or propylene by the formation of π complexes of platinum(II) as active centers in the surface layer under these conditions. The controlling stage of the catalytic reaction is chloroplatination of the π-coordinated acetylene by the HCl molecule. The reaction takes place as a concerted process, in which an intermediate β-chlorovinyl derivative of platinum(II), a complex of platinum with a coordination vacancy[PtCl ₃ ^* ]⁻, and a new molecule of HCl are formed simultaneously with cleavage of the H—Cl and Pt—Cl bonds in the metal complex adjacent to the π-acetylene complex. The catalytic cycle closes with rapid dissociation of the organoplatinum intermediate by the action of HCl, giving the final product and the initial complex [PtCl₄]²⁻. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 5, pp. 306–311, September–October, 2006.     

Catalytic hydrochlorination of acetylene on PdCl<Subscript>2</Subscript>/C supported catalysts: Kinetic isotopic effect of HCl/DCl,stereoselectivity, and mechanism

Two routes of catalytic hydrochlorination of acetylene were found by the isotopic label method for systems with supported palladium K₂PdCl₄/C and Н₂PdCl₄/C catalysts: with formation of the products of syn- and anti-addition of the H(D)Cl molecule to the triple bond of acetylene. Two isotopic effects that differ in magnitude were determined for these systems from the reaction kinetics and the ratio of the yields of the nondeuterated and monodeuterated isotopomers of the product, which are due to the participation of the H(D)Cl molecule in the two reaction stages: limiting chloropalladation and rapid protodemetallation. The effective activation energies and kinetic isotope effects coincided within the experimental errors, which suggests that the reaction mechanisms are similar and the active centers of the catalysts in systems with K₂PdCl₄/C and Н₂PdCl₄/C are of the same nature.     

Catalytic hydrochlorination of acetylene on mechanochemically-activated K<Subscript>2</Subscript>PdCl<Subscript>4</Subscript>

We report the catalysis of the hydrochlorination of acetylene on the surface of dry K₂PdCl₄ subjected to prior mechanical activation in an atmosphere of acetylene or propylene. The stereochemistry of the reaction corresponds to trans addition of the halogen and hydrogen atoms to the C-C triple bond. The hydrogen halide is the source of the halogen atom in the reaction product. The mechanical activation of K₂PdCl₄, in contrast to the case of K₂PtCl₄, is also capable of activating the C-C double bond: propylene is hydrochlorinated under similar conditions to isopropyl chloride. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 44, No. 5, pp. 306–309, September–October, 2008.     

Platinum-catalyzed addition of iodomethane to acetylene

The reaction of iodomethane and acetylene in the presence of Pt^II and NaI in acetone gives (E)-1-iodopropene. A possible mechanism involves the intermediate formation of a Pt^IV methyl vinyl derivative by the iodoplatination of acetylene with a reversibly formed a Pt^IV methyl complex and assumes the catalytic character of the process.     

Solvent-specific reduction of Na<Subscript>2</Subscript>PtI<Subscript>6</Subscript> in acetone

Oxidation state of iodide complexes of Pt^II and Pt^IV in large excess of NaI with respect to platinum in water and acetone solution has been determined by means of ¹⁹⁵Pt NMR spectroscopy. In acetone, iodide complexes of Pt^IV are almost quantitatively reduced into Pt^II, and iodine is bound in a poorly soluble polymeric complex with sodium iodide and acetone. Iodometric titration has revealed the formation of equivalent amount of iodine. Reduction of platinum has not been observed in aqueous medium.     

Effect of Tail Gas Recirculation Mode on the Activity and Selectivity of the Сo/SiO2 Catalyst for Fischer‒Tropsch Synthesis

Kinetics and Catalysis - The effect of the gas recirculation mode on the selectivity and deactivation rate of the Co-Al2O3/SiO2 catalyst of the Fischer?Tropsch synthesis at high pressure (6...     

Effect of mechanicochemical treatment on the activity of K<Subscript>2</Subscript>PdCl<Subscript>4</Subscript> in the heterogeneous catalytic hydrochlorination of acetylene

A heterogeneous catalyst for the hydrochlorination of acetylene using gaseous HCl was obtained by prior mechanical activation of K₂PdCl₄ powder in an atmosphere of acetylene or propylene. Active sites are formed during the mechanical treatment in the surface layers of the catalyst, which are Pd(II) complexes with a coordination vacancy.